Restrictor tube for refrigerating systems



Jan. 6, 1948.

D. NEWMAN HESTRICTOR TUBE FOR REFRIGERATING SYSTEIIS Filed July 18, 1945 HiSAttorney.

E l 1 y Inventor Delbert? Newman,

Figi

Patented 1.... a. 1 948 RE STRICTOR TUBE FOR REFRIGERATING" SYSTEMS v Delbert F. Newman, Schenectady; N. Y., assignor to General Electric Company, a corporation of New York Application July 18. 1945, Serial No. 605,810

3 Claims. 1

My invention relates to mechanical refrigerating systems employing fixed restrictors for controlling the fiow of refrigerant to the evaporating element, and relates particularly to the prevention of the clogging of such restrictors by the freezing of water therein,

When a restrictor tube of so-called capillary tube is employed to control the flow of liquefied refrigerant to the evaporator of a refrigerating machine, it sometimes happens that, minute quantities of water in the system freeze in the tube and restrict the 'normal flow of refrigerant therethrough. It has been found'that extended operation of refrigerating machines having hermetically sealed motors may result in the formation or collection of small quantities of water in the refrigerant circuit. When a refrigerant is employed in which the' water is not chemically absorbed, the water tends to condense and be frozen in the low temperature portions of the system. When the temperature in the restrictor tube falls below the freezing point of water therein, the water freezes in the restrictor and interferes with the normal operation of. the machine, sometimes blocking the tube completely and stopping the flow of refrigerant. Accordingly, it is an object of my invention to provide a refrigerating system employing a restrictor tube as a flow controlling device and including an improved arrangement for preventing the blocking of refrigerant flow by'the freezing of water in the tube.

Further objects and advantages of my invention will become'apparent as the following description proceeds and the features of novelty which characterize my invention'will be pointed out with particularity in the claims annexed to and forming part of this specification,

Forv a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. 1 is a front elevation view partly insection of the upper portion'of a household refrigerator including a refrigerating machine embodying my invention; Fig. 2 is an enlarged view of a portion of the restrictor tube of the refrigerating machine shown in Fig. 1; and Figs. 3 and 4 are views similar to Fig. 2 showing further modifications of my invention.

Referring now to the drawing, the household refrigerator illustrated in Fig. 1 includes a cabinet i having a food compartment 2 cooled by a refrigerant evaporating unit or evaporator 3 of the flooded type having refrigerant'circulating conduits or louvers formed in its side walls in a manner well known to the art and provided with a liquid and vapor separating header 4 in the upper portion thereof. A refrigerant liquefying unit 5 is mounted in a housing 6 on top of the cabinet I.

- The liquefying unit includes a hermetically sealed 6 casing 1 within which are arranged a refrigerant compressor and an electric driving motor. The compressed refrigerant is discharged through a connection 8 and flows to a condenser 9 where it is liquefied by. air circulated over the surface 10 of the condenser by a fan'(not shown) but driven by a motor Ill. The liquefied refrigerant is supplied from the condenser through a restrictor tube II and flows through the tube to the evaporator which it enters at a, connection l2. Refrigerant l5 vaporized in the evaporator is withdrawn therefrom through a suction line l3 and returned to the motor compressor easing 1. The suction line l3 and the greater portion of the restrictor tube II are secured together in heat exchange relationship to provide a transfer of heat'from the warm liquid refrigerant to thecold vaporized refrigerant being returned to the compressor. During the operation of the refrigerating machine, liquid refrigerant in the evaporator 3, that is, in the low pressure side of the refrigerating system, is'vaporized by the absorption of heat fromthe contents of the food storage compartment 2, the vaporized refrigerant being returned to the liquefyl-ng unit 5 in the high pressure side 80 of the refrigerating system where the heat is removed and discharged to the air circulated over the condenser. The warm liquid refrigerant at high pressure. enters the restrictor tube l I and the pressure is reduced as the refrigerant flows through the tube to the evaporator. This reduc-- tion in pressure is such that during the normal operation of the system the refrigerant in the tube reaches a temperature below the freezing point of water within the tube. Should it happen 40 thatwater is present in the refrigerant, ,this water may freeze in the tube and tend to restrict the tube and even stop the flow of refrigerant.

Flow restricting tubes, such as the tube ll are designed to pass the'required amount of liquid refrigerant under the temperature and pressure conditions prevailing during therange of ambient temperatures for which the refrigerating system is designed. The internal diameter of ti e tube and its length are also preferably such that the 60 flow of gaseous refrigerant is relatively restricted, it-being desirable to provide sufllcient resistance to the flow of gas to enable a refrigerating ma chine to attain quickly after starting the required pressure difference between the high and low sides thereof. It has been found that restrictor tubes designed to provide operation in this manner occasionally are plugged by the freezing of moisture within the tube, thereby preventing operation of the refrigerating system until the plug has been removed. During the manufacture of hermetically sealed refrigerating systems, extensive precautions are taken to eliminate mois-i ture and the machines are dried as thoroughly as possible before being sealed. However, after operation under heavy load conditions for a long period of time, water vapor may appear in the system. This water vapor may, for example, be the result of high temperature operation of the electric motor windings which are provided with cotton insulation. Refrigerating machines which develop trouble because of the formation of water vapor may be stopped by freezing of the water in the restrictor tube; however, since the ice melts upon a rise in temperature it may happen that the machine which has been stopped by freezing thereafter runs for a considerable period of time before it is stopped again in a manner to plug the restrictor tube. The operation of the machine therefore becomes undependable and may result in frequent calls for service because of the inability of the machine to maintain the required temperatures in the refrigerator cabinet.

The quantities of water present inrefrigerating machines are very small, but are sufllcient to freeze and plug the conventional restrictor or capillary tube. I have found that the plugging of restrictor tubes due to the presence of this water may be sufficiently minimized or eliminated by constructing a portion of the restrictor tube toward the outlet end thereof to have an increased cross sectional ,area. For example, as shown in Fig, 2 the retrictor tube II is provided with an enlarged portion H on the lower end thereof which extends from the evaporator back to the portion of thetube II which is soldered in heat exchange with the suction line 13. In Fig- 2 the major portion ofthe section It has been formed as a coil within the insulating material of the top wall of the cabinet. A portion of the section It between the evaporator connection I! i and the coil is secured by clip l5 to the .suction line l3 as a support. During the operation of the refrigerating machine shown in the drawing, the restrictor tube H, including the portion l4,

operates in the usual manner to determine the rate of flow of refrigerant from the condenser to the evaporator.- The section It is made of sumcient length to provide a substantial portion of the pressure drop throughout the tube, and its length and diameter are selected so that, throughout the range of operating conditions ofthe machine, substantially the entire temperature drop from 32 F. down to the temperature of the oval orator is attained within the section M. It will be apparent, therefore, that when the refrigerant and any water contained therein reach the freezing point of water within the tube, it is within the larger diameter portion ll ofthe tube and the increased area is such that the small amount of water in the system is insufllcient to freeze and plug the larger cross sectional area of the section H. I have found that with a relatively small increase in the diameter of the portion l4 over that of the main portion of the tube ll there is provided a combined tube which will not be plugged by the freezing of water normally formed during the operation of the refrigerating machine over a period of many years. The provision of this type of tube therefore eliminates the danger of plugging and renders the refrigerating machine reliable in operation over a long period of time without dan er of stoppage.

diameter of 41 thousandths of an inch. In .one

such machine the smaller diameter section of the tube was ten feet long and the larger diameter section two feet long.

In Fig. 3 the restrictor tube I l is'pro'vided with an enlarged portion taking the place of the portion [4 in Fig. 2 and comprising a portion l6 of a slightly larger diameter than the main tube and a portion of slightly larger diameter than the portion l6, and in Fig. 4 the second section of the tube has been constructed with its internal diameter increasing gradually from that of the main section, it being provided with a tapered section I. corresponding to the section l4 of Fig. 2. The

- stepped increase in diameter in the modification of Fig. 3 and the gradual increase in diameter of the modification of Fig. 4 both provide increased nection with a specific type of compression refrigerating machine, other applications will readily be apparent to those skilled in the art. I do not. therefore, desire my invention to be limited to the particular construction illustrated and described and I intend by the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a refrigerating system having high pressure and low pressure sides and including a refrigerant evaporating unit and a refrigerant liquefying unit connected in a closed circuit, said evaporating unit and said liquefying unit being on the low and the high pressure sides respectively of said system, a restrictor tube in said circult separating said high and said low pressure sides for controlling the flow of refrigerant from said liquefying unit to said evaporating unit, the pressure drop through said tube during normal operation of said system being such that the temperature of refrigerant flowing through said tube falls below the freezing point of water in the tube before being discharged therefrom, said tube including a. first section comprising the major portion of the length of said tube and a second sec-- evaporatingunit and said liquefying unit being on the low and the high pressure sides respectively of said system, a restrictor tube in saidgcircuit separating said high and said low pressure sides for controlling the flow of refrigerant from said iiquefying unit to said evaporating unit. the pressure drop through said tube during normal operation 01' said system being such that the temperature of refrigerant flowing through said tube falls.

below the freezing point of water in the tube before being discharged therefrom, said tube including a first section comprising the major portion of the length or said tube and a second section having a cross sectional area increasing gradually from that of said first section toward the'outlet of said tube, the relative lengths and cross sectional areas of said sections of saidtube being such that substantially the entire temperature drop from 32 F. down throughout the normal range of operation of said system occurs in said second section of said tube.

3. In a refrigerating system having high pressure and low pressure sides and including a retrigerant evaporating unit and a refrigerant liquefying unit connected in a closed circuit, said evaporating unit and said liquefying unit being on the low and the high pressure sides respectively of said system,'a restrictor tube in said circuit separating said-high and said low pressure sides for controlling the flow of refrigerant from said iiquefying unit to said evaporating unit, the pressure drop through said tube during normal opera- 6 ture of refrigerant flowing through said tube falls below the freezing point of water in the tube before being discharged therefrom, said tube including a first section comprising the major portion of the length of said tube and a second sec- REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name 1 Date 2,192,850 Tobey Mai. 5, 1940 2,280,202 Tobey Apr. 21, 1942 2,187,662 Pigott Jan. 16, 1940 FOREIGN PATENTS Number Country I Date 114,159 Switzerland Mar. 1, 1926 Great Britain Oct. 24, 1896 

